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The Many Forces Driving Extinction

By Andrew C. Revkin May 19, 2011 1:17 pmMay 19, 2011 1:17 pm

Among the many valuable comments that have come in so far on my piece about disputes over extinction rates, one deserves special attention. It comes from Joseph R. Mendelson III of Zoo Atlanta, whose work on vanishing frogs is the subject of an upcoming piece here.

A particular focus of his is Rabbs’ fringe-limbed treefrog. There are only two known living specimens, both refugees from a place in Panama devastated — like so many other amphibian habitats — by the spreading chytrid fungus. One frog is at the Atlanta Botanical Garden and the one below at Zoo Atlanta. None have been heard calling in their home range since 2007. Both captive specimens are male. At the end of this post you can read what Mendelson has written about that terminal state of affairs.

Mendelson’s comment was made in an e-mail exchange I initiated with a batch of biologists focused on the rare and vanished:

Most of you likely don’t know me. I dwell on extinctions quite a bit these days. I cannot claim mastery of the equations being debated here, but I find the focus on habitat loss as the driver of extinction to be narrow minded. I don’t see the utility of focusing so much attention on arguing the quantification/estimation of extinction rates as a result solely of habitat loss.

The recent world (e.g., bats, bees, amphibians, corals) is showing us that there are far more pernicious forces at work, viz., emerging infectious diseases, climate change, agrochemicals. If nothing else, my career has shown me that the most wholly protected habitats on the planet are now devoid of a good percentage of their native flora and fauna.

Habitat protection, while crucially important, is not working and we conservationists seem to be the last to admit this. I know my message is often misinterpreted — I once signed in at a reception at The Nature Conservancy only to have the receptionist look up suddenly at say “Oh, Joe Mendelson — aren’t you the one saying we no longer need to preserve habitats?”

For the record: I have never said that.

A specific point, in response to John Alroy’s dead-on comment:

“Only in retrospect, when some future culture — human or otherwise — examines the fossil record, will the die-off be evident as a substantial pruning of the branches of the tree of life, he said. ”For the entire remaining duration of life on earth,” he said, ”this event we’re responsible for is clearly going to show up as a signature.”

I will add that this fossil record that we assume we are in the process of creating is more immediate than most of us realize. Much of it is not in the recent geological strata, but rather on the shelves of our natural history museums.

Hence the novel endeavor of “Forensic Taxonomy” that I describe in a recent essay — and where my colleagues in amphibian taxonomy and myself find ourselves in this age.

Here’s an excerpt from Mendelson’s must-read essay on the inevitable end game for the Rabbs’ treefrog:

There is no female that we know of, and one morning I will find the male at Zoo Atlanta dead of natural causes. I will collect tissue samples for phylogenetic studies, I will collect cells for San Diego Zoo’s Frozen Zoo initiative (perhaps one day it can be cloned?), and then I will preserve the specimen for the museum shelf.

Shall I post a video clip on YouTube so people can watch the frog move about, like the famous film clip of the last thylacine? Then I will return to my lab, take a jar off the shelf and proceed to describe another new species of frog that used to exist somewhere in the world.

Here’s the YouTube video he mentions, of the last known Tasmanian tiger:

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By 2050 or so, the human population is expected to pass nine billion. Those billions will be seeking food, water and other resources on a planet where humans are already shaping climate and the web of life. Dot Earth was created by Andrew Revkin in October 2007 -- in part with support from a John Simon Guggenheim Fellowship -- to explore ways to balance human needs and the planet's limits.